Capacitors for use in electronic instruments such as portable telephone and personal computer are demanded to have a small size and a large capacitance. Among these capacitors, tantalum capacitors are preferred because of their large capacitance for the size and good performance. For the dielectric material of tantalum electrolytic capacitors, tantalum oxide is usually used but in order to more increase the capacitance, studies are being made on niobium electrolytic capacitors using niobium oxide having a higher dielectric constant for the dielectric material. The present inventor has previously revealed that among niobium electrolytic capacitors, electrolytic capacitors using a partially nitrided niobium sintered body for the electrode have a large capacitance and good LC characteristics (see, JP-A-10-242004 (U.S. Pat. No. 6,115,235) (the term “JP-A” as used herein means an “unexamined published Japanese patent application)).
The capacitor manufactured using a partially nitrided niobium sintered body disclosed in this patent publication has a large capacitance and good LC characteristics but undergoes great reduction in the capacitance due to application of DC bias. Accordingly, for obtaining a capacitor having a desired capacitance, it is necessary to use the sintered body in a large amount or produce a sintered body using niobium powder having a smaller particle size.
Accordingly, the object of the present invention is to provide a capacitor having good LC characteristics and undergoing less reduction in the capacitance due to application of DC bias, and a production process therefor.
The reduction in the capacitance due to application of DC bias is a property peculiar to niobium and this is presumed to occur because the niobium oxide as a main component of the dielectric layer is unstable.